A conventional circuit for suppressing noise produced in reception of stereo broadcasting is known as a Hi-blend circuit. One such Hi-blend circuit is disclosed in Japanese patent Post-Examination No. 45-32282.
Using this Hi-blend circuit, in the case of FM stereo broadcasting, two halves of a noise component N of a stereo differential signal (L-R) in a composite signal exist in demodulated L and R signals, respectively. These two halves of the noise component N exist in such a state that the halves are in antiphase to each other. In this circuit, only the high band components of the L and R signals are added to each other, thereby cancelling the antiphase halves of the noise component N with each other, and eliminating jarring noise in a high band component.
Although the above-mentioned conventional Hi-blend circuit has a noise reduction effect on high band signal components, this circuit does not act on middle and low band signal components. Accordingly there has been a problem with the conventional Hi-blend circuit in that noise cannot be eliminated over a broad range from a low band to a high band. Moreover, there has been a further problem in that it is impossible to obtain a satisfactory stereo sense because a stereo signal becomes perfectly monaural in a high band with the Hi-blend circuit so that separation of the right and left signals is deteriorated.